Nanocrystalline materials

ABSTRACT

A method and system for synthesizing nanocrystalline material. A system includes a chamber, a nonconsumable cathode shielded against chemical reaction by a working gas not including an oxidizing gas, but including an inert gas, a consumable anode vaporizable by an arc formed between the cathode and the anode, and a nozzle for injecting at least one of a quench and reaction gas in the boundaries of the arc.

This application is a continuation of Ser. No. 08/286,063 filed Aug. 4,1994, U.S. Pat. No. 5,514,349 which is a division of Ser. No. 08/097,884filed Jul. 27, 1993 U.S. Pat. No. 5,460,701.

The present invention is concerned generally with a method of making ananostructured material. More particularly, the invention is concernedwith a method of making a variety of stoichiometric-nanostructuredmaterials by controlling the working gas composition in a plasma arcsystem. The production rate of nanostructured material can also besubstantially enhanced by combining N₂ or H₂ gas with Ar working gas.

In the recent past, it has been shown that nanostructured materialsexhibit enhanced or unique properties compared to typicalpolycrystalline materials. For example, metallic nanostructuredmaterials can be sintered at low temperatures but exhibit higherhardness and yield strength than polycrystalline metallic materials.Ceramic nanostructured materials exhibit much greater ductility at lowtemperatures compared to conventional ceramic materials. In order tomanufacture such nanostructured materials, it is necessary to controlthe particle size and chemical stoichiometry. However, in order toprepare commercial quantities of these nanostructured materials, theprocess must also allow rapid production while controlling the chemistryand particle size. Current methods of manufacture do enable some controlof particle size but cannot reliably control the chemical stoichiometryor rapidly manufacture the material in large quantities while alsocontrolling the particle size and stoichiometry.

It is therefore an object of the invention to provide an improved methodand article of manufacture of nanostructured material.

It is also an object of the invention to provide a novel method ofmanufacturing a nanostructured material of controlled stoichiometry.

It is another object of the invention to provide an improved method ofproducing large quantities of nanostructured materials of wellcontrolled particle size and chemical stoichiometry.

It is a further object of the invention to provide a novel article ofmanufacture of nanostructured material of well defined, very small gainsize.

It is an additional object of the invention to provide an improvedmethod and article of manufacture of nanostructured gamma ferrite.

It is still another object of the invention to provide a novel method ofmanufacturing a nanostructured material of controlled particle sizeusing working gas mixtures of argon and nitrogen and/or hydrogen and/ora carbon containing gas.

It is yet a further object of the invention to provide an improvedmethod of controlling nanostructured grain size by controlling theamount and variety of quench gas injected into a reaction zone of aplasma arc system.

It is yet an additional object of the invention to provide a novelmethod of controlling manufacture of nanostructured material by controlof color and intensity of light output by the reaction zone, cathodezone and anode zone of a plasma arc system.

It is also a further object of the invention to provide an improvedmethod of generating stoichiometric Al₂ O₃, ZrO₂, TiO₂ and Fe₂ O₃ andnanostructured material.

It is still an additional object of the invention to provide a novelmethod of controlling production of nanostructured material bycontrolled adjustment of working gas and quench gas injection locationin a plasma arc system.

It is yet another object of the invention to provide an improved methodof controlling pore size distribution and pore size spacing of ananostructured material.

These and other objects and advantages of the invention will becomeapparent from the following description including the drawings describedhereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is one embodiment of a plasma arc system constructed inaccordance with the invention and;

FIG. 2 is another embodiment of the system;

FIG. 3 illustrates one embodiment of gas injection nozzles for theplasma arc system and;

FIG. 4 shows another gas injection nozzle embodiment;

FIG. 5A shows an X-ray diffraction plot of a TiN nanostuctured materialand;

FIG. 5B shows an X-ray plot of a TiO₂ nanostructured material;

FIG. 6A is an energy dispersive X-ray analysis output for a titaniumoxide prepared without oxygen present in the working arc; and

FIG. 6B for a titanium oxide prepared with oxygen in the working gas;

FIG. 7 illustrates a top view of a nozzle for turbulent mixing of ananocrystal aerosol using tangentially injected gas; and

FIG. 8 shows the mixing nozzle with radially injected gas;

FIG. 9 is a mixing nozzle for receiving nanocrystalline aerosol from aplurality of sources;

FIG. 10 is a graph of quench/reaction gas flow rate into a mixing nozzleversus nanocrystalline particle diameter;

FIG. 11A is a graph of nanocrystalline particle size versus gas quenchflow rate into the plasma tail flame;

FIG. 11B is the nanocrystalline particle size versus quench/reaction gasinjection point relative to the molten anode position; and

FIG. 11C is titania production rate; and

FIG. 12A shows particle size distribution for nanocrystalline materialprepared in accordance with the invention as compared to a prior artmethod;

FIG. 12B illustrates pore volume versus pore diameter fornanocrystalline material prepared in accordance with the invention ascompared to a prior art method;

FIG. 12C shows the pore size spacing distribution for a nanocrystallinematerial prepared in accordance with the invention; and

FIG. 12D shows the small angle neutron scattering characteristic ofnanocrystalline material before treatment and after treatment to formthe pore array of controlled spacing.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A plasma arc system constructed in accordance with the invention isshown generally in FIG. 1 at 10. The preparation of nanostuctured, ornanocrystalline, material begins with the vaporization of a high purityprecursor material 12 in a chamber 14 via an arc generated, for example,by a water-cooled TIG (tungsten inert gas) torch 16 driven by a powersupply 18. The interior of the chamber 14 is preferably maintained at arelative pressure of about 20 inches of mercury vacuum up to +3 psipositive pressure (absolute pressure 250 torr to 1000 torr).

The precursor material 12 is melted and vaporized by the transfer of arcenergy from a nonconsumable electrode, such as a tungsten electrode 20with 2% thorium oxide. The nonconsumable tungsten electrode 20 isshielded by a stream of an inert working gas 22 from reservoir 25 tocreate the arc. The working gas 22 acts to shield the nonconsumabletungsten electrode 20 from an oxidizing environment and then becomes aworking plasma gas when it is ionized to a concentration large enough toestablish an arc. The inert working gas 22 preferably contains argon andis directed by a water cooled nozzle 24 attached to the torch 16.

The consumable precursor material 12 is, for example, in the form of arod which has a diameter of 0.0625" to 2" diameter and is fedhorizontally (see FIG. 1A) or vertically (see FIG. 1B) relative to thenonconsumable tungsten electrode 20. The feed rod precursor material 12is continuously fed to allow a stable arc and continuous production ofnanocrystalline material. A continuous production is preferred overbatch operation because the process can be run on a more consistentbasis. The precursor material 12 is electrically grounded and cooled bya copper anode 28, and the precursor material 12 is given bothtranslational and rotational motion.

The nonconsumable tungsten electrode 20 is preferably inclined at anangle so as to create an elongated arc plasma tail flame 30. Dependingon the current level the plasma tail flame 30 can be about one toseveral inches long. The plasma tail flame 30 acts as a high temperaturegradient furnace into which the vaporized precursor material 12 isinjected along with a quench and/or reaction gas 32 (hereinafter,"quench/reaction gas"), if desired, through the nozzle 35. The amount ofthe quench/reaction gas 32 injected into the plasma tail flame 30 iscontrolled by a flow meter 36 having regulator 31 as in the case of theworking gas reservoir 25. A concentric gas injection geometry isestablished around the plasma tail flame 30 to allow homogeneousinsertion of the quench/reaction gas 32. Preferably the nozzle 35 is oneof an arrangement of nozzles 37 as shown in FIG. 2. The quench/reactiongas nozzles 37 can be positioned at any point along the length of theplasma tail flame 30 as shown in FIG. 1. The insertion location of thequench/reaction gas 32 can act to truncate the length of the plasma tailflame 30 and allow control of the manufacturing process. The quench andreaction gas composition preferably is one of oxygen, nitrogen, helium,air or combinations of these gases.

The plasma arc system 10 can be used to manufacture a variety ofnanostructured material. For example, titanium metal vapor in the plasmatail flame 30 can be reacted with nitrogen gas to form 8-25 nm TiNnanocrystals. Titanium metal can also be reacted with oxygen gas to form5-40 nm TiO₂ nanocrystals (see the Examples). X-ray diffraction data ofthe two Ti based ceramic materials TiN (FIG. 3A) and TiO₂ (FIG. 3B) showthat two distinct materials are formed using the plasma tail flame 30 asa reaction zone. Transmission electron microscopy also shows distinctlydifferent morphologies for the two materials.

To increase the temperature gradient in the plasma tail flame 30 andincrease its length, a dissociable inert gas (such as, nitrogen,hydrogen or both) can be mixed (1-70%) with the working gas 22 whichshields the nonconsumable tungsten electrode 20. A higher temperature inthe plasma tail flame 30 allows for a more complete reaction of theprecursor material 12 with the reaction gas 32. In addition, control ofthe point of injection can be used to control the completeness ofreaction of the precursor material 12. The large temperature gradientalso can control the nanocrystal formation (size and distribution) andthe degree to which the nanocrystals agglomerate. Unlike prior art (suchas in U.S. Pat. No. 4,732,369), dissociable oxygen gas is mostpreferably not used in the working gas (termed "pinch gas" in U.S. Pat.No. 4,732,369) because it causes erosion of the nonconsumable tungstenelectrode 20 and generates tungsten impurities in the final product.FIG. 4 shows an energy dispersive X-ray analysis of material madewithout (FIG. 4A) and with (FIG. 4B) 0.5% oxygen present in the workinggas 22. It is apparent that even a small amount of oxygen (>0.5%) in theworking gas 22 can cause tungsten impurities at levels of about 0.2% inthe final product Inductively coupled plasma mass spectrometry impurityanalysis shows that the materials made by this process, and not usingoxygen in the working gas 22, are very pure. Table 1 shows the typicalimpurities present in materials made by this preferred method.

                  TABLE 1    ______________________________________    % mass impurities in Al.sub.2 O.sub.3 (99.9092%)    ______________________________________    Na    Mg      Si     K     Ca    Ti    Fe    Cu    ______________________________________    0.0063          0.0038  0.018  0.0051                               0.0094                                     0.0010                                           0.0400                                                 0.0072    ______________________________________    % mass impurities in TiO.sub.2 (99.9226%)    ______________________________________    Al    Mn      Si     K     Ca    Ni    Fe    Cu    ______________________________________    0.0233 0.0021             0.0047  0.0051  0.0048                                   0.0052                                         0.0290                                               0.0032    ______________________________________

Once a nanocrystal aerosol 40 (see FIG. 2) is formed by thequench/reaction gas 32, the agglomeration of the nanocrystals takesplace. At this point the aerosol 40 is turbulently mixed in a reducingcone-shaped nozzle 42 to prevent further agglomeration. Recirculated gasor room air 44 is introduced by blower 46 into the cone-shaped nozzle42. The recirculated gas 44 can be injected into the nozzle 42 radially(see FIG. 5B) or tangentially (FIG. 5A) by a gas inlet head 48. Theswirling motion of the gas 44 generated in the cone-shaped nozzle 42mixes and dilutes the aerosol 40 with the cool recirculated gas 44 toprevent further agglomeration of the nanocrystals. The cone-shapednozzle 42 can also be used to blend and homogenize the nanocrystalaerosol 40 generated by one or more sources 43 as shown in FIG. 6. Thesources 43 can be of the same material to increase production rates orindividual sources generating a different material allowing theformation of composites.

As best seen in FIG. 1, after leaving the cone-shaped nozzle 42, a mixedaerosol 45 is rapidly expanded into a large volume collector housing 50by the action of the blower 46. The expansion of the gas allows furthercooling of the aerosol 45. A temperature decrease of several hundreddegrees has been measured after expansion of the gas. The largecollector housing 50 contains a filtering media 54. The filtering media54 traps the weakly agglomerated nanocrystals, and the gases areseparated through the filtering media 54 by the blower 46. Thenanocrystals remain on the filtering media 54 until they are released bya gas pulse from gas jet source 56. The filtering media 54 can be poroussintered metal or cloth fibers with a temperature resistant coating. Theagglomerated nanocrystals behave as conventional powders; and once freedfrom the filtering media 54, the powders are gravitationally collectedin a storage vessel 58 through a valve 60.

The quality of the nanostructured material (average particle size, sizedistribution, purity and degree of agglomeration) can be controlled bythe point at which the quench/reaction gas 32 is injected, and thedilution of the nanocrystal aerosol 40 can be made soon after formationof the particles. In FIG. 7 is shown the agglomerate particle sizeversus the amount of the quench/reaction gas 32 that is radially ortangentially injected into the cone-shaped mixing nozzle 42. In manyinstances the quench/reaction gas 32 can be injected at the same pointdepending on the arc current and precursor material. The quench/reactiongas 32 is preferably injected into the plasma tail flame 30 at the pointwhere the temperature is such that nucleation and condensation havetheir onset. At any point in the plasma tail flame 30 there is a balancebetween condensation and evaporation of the embryonic crystallites.Analytically, this critical particle size is expressed with thefollowing temperature and material property dependence, ##EQU1## whered_(c) is the critical particle diameter, γ is the surface tension (N/m),V_(a) is the atomic volume (m³), k is Boltzman's constant (1.38×10⁻²³J/K), T is the temperature (K), and P_(V) and P_(O) are the actual andequilibrium vapor pressure (N/m²). Without limiting the scope of theclaims, these particles are believed to act as monomers for growth intolarge particles via coalescence with other monomers or small particles.The amount of coalescence growth is dependent on the number ofcollisions the monomers experience. Because the temperature gradient isvery large in the plasma tail flame 30, the vapor and the formingparticles move with great velocity. The velocity in the plasma tailflame 30 is highly dependent on the arc characteristics, ##EQU2## wherev is the velocity (m/s), 1 is the arc current (A), J is the currentdensity (A/m²), μ_(O) is the free space permeability (1.256×10⁻⁸ N/A²),ρ is the vapor density (kg/m⁻³). Critical particles can be cooledquickly by injecting the quench/reaction gas 32 at the appropriatelocation where the monomers form, and the number of monomer collisionscan be reduced by dilution with an optimal amount of the quench/reactiongas 32. This control measure can allow achievement of the desired smallparticle size. Because the velocity component varies as r^(-1/2), theamount of the quench/reaction gas 32 injected can become more importantthan the point of gas injection. However, as production rates increase(and hence vapor density increases), both the amount and location ofinjection of the quench/reaction gas 32 become important. In FIG. 8A isshown the average particle size as a function of the amount of thequench/reaction gas 32 injected into the plasma tail flame 30, and FIG.8B illustrates the effect of the injection location of thequench/reaction gas 32 upon the nanocrystalline particle diameter.

The reaction gas can be introduced with the quench gas or separately inorder to form an oxide, carbide or nitride from the metallic orsemiconducting precursor material (e.g., precursor Si can be used toform SiO₂, Si₃ N₄, or SiC). Introducing the reaction gas with the quenchgas into the plasma tail flame 30 allows the formation of a highermelting point material which enhances the quenching process and enhancesthe formation of small nanocrystal particles. Also, using a dissociablegas, for example, H₂ or N₂, in the working gas 22 allows the plasma tailflame 30 to reach a higher temperature which allows a more completereaction of the precursor vapor.

When pure argon is used as the working gas 22 and oxygen is used as thereaction gas 32 and injected into the plasma tail flame 30, asubstoichiometric (oxygen deficient) metal oxide nanocrystal product isformed. The substoichiometry can be detected by Raman spectroscopy,X-ray diffraction or thermo gravimetric analysis. The substoichiometricmaterial requires post processing to achieve complete oxidation. Thepost processing usually involves annealing the powder at hightemperature in air. This step often increases the degree ofagglomeration and causes particles to grow in size. With the addition of5-50% hydrogen to the working gas 22 (particularly Ar gas), the formednanocrystal product can be made filly stoichiometric; and the productrequires no post processing. This gas mixture reduces cost inmanufacturing the nanostructured material and allows the formation of aweakly agglomerated material. The effect this has on particle size isquite substantial. By fully reacting the material during synthesis,nanocrystals are weakly agglomerated and range in size from 15-20nanometers, whereas those particles that require post reaction will ingeneral end up being 30-50 nanometers in diameter.

The nanocrystals formed by the process described herein can be testedfor their ability to form a nanostructured material. There are varioustechniques for making ultrafine, nanometer sized particles; however, thedegree of agglomeration is critical when bulk nanostructures ornanometer dispersions are desired. If agglomeration is too strong,practical mechanical forces are not sufficient to break down theagglomerates into primary or near primary particles. A high energyprocess like ball milling can be used to break down the particles.However, the ball milling step often introduces contaminants into thematerial and reduces purity.

Two techniques are commonly used to measure particle sizes in thenanometer range; transmission electron microscopy (TEM) and BET surfacearea measurements. TEM yields a visual inspection of the individualcrystallites that agglomerate into particles and BET infers an averageparticle size from a surface area measurement using the formula,##EQU3## where d is the mean particle diameter, ρ is the specificgravity of the material (kg/m³) and S is the measured specific surfacearea (m² /gm). If the crystallites are weakly agglomerated, formingsmall necks between the crystallites, and the crystallites are equiaxed,nearly spherical in shape, then TEM and BET average particle sizesshould be nearly identical. The average TEM crystallite size, and theaverage BET particle size should be within 30% of each other in order tohave weak enough agglomeration to form a nanostructured material. Thenanocrystals generated in the process show a much smaller average sizeand a narrow size distribution relative to other prior art methods formaking nanocrystalline materials (i.e., U.S. Pat. No. 4,642,207).

Table 2 shows a comparison of aluminum oxide and zirconium oxidegenerated by the instant process and by the process in U.S. Pat. No.4,642,207. Although both processes use arc energy to generate a vapor ofthe precursor, the modifications of this instant process yield betternanocrystalline material with smaller particle size and narrower sizedistribution. It should also be noted that a smaller size distributionhas been obtained without the addition of a high frequency inductionplasma like that used in U.S. Pat. No. 4,732,369.

                  TABLE 2    ______________________________________              Preferred           Uda et. al.              form of invention   U.S. Patent 4642207    material  avg. size                       width      avg. size                                         width    ______________________________________    ZrO.sub.2 8        2-25       --     20-200    Al.sub.2 O.sub.3              18       8-50       38     10-100    ______________________________________     (all sizes are in nanometers)

The degree of the agglomeration in nanostructured materials can bemeasured by either bulk consolidation of the nanocrystals or bydispersion of the nanocrystals. Consolidation testing of the nanocrystalpowders is achieved by placing a suitable amount of nanocrystallinepowder into a die and punch apparatus and applying pressure in the rangeof 1000-40,000 psi to the punches. The resultant pellet is nanostucturedif it has a pore size distribution that is similar to the grain sizedistribution. Materials that are optically transparent in the bulksingle crystal state will also be transparent as a nanostructuredmaterial since the grains and pores of the material are much smallerthan the wavelength of visible light (i.e., below 50 nm). The BET andTEM average particle sizes are shown in Table 3 along with the averagepore size and distribution width. A transparent sample can be obtainedby consolidating nanocrystals with a weak degree of agglomeration. Anopaque sample results if prepared from nanocrystals with stronger(harder) agglomeration, forming a material with small grains, but largepores. Agglomeration is controlled by the injection location in thechamber 14 and the amount of the quench/reaction gas 32 injected, andthe amount of gas injected into the cone-shaped mixing nozzle 42. Thistype of porosity can be difficult to remove by conventional sinteringprocesses.

                  TABLE 3    ______________________________________            all sizes are in nanometers            TEM        BET    sample  crystallite size                       particle size                                 avg. pore size                                          pore range    ______________________________________    transparent            8          9         5        1-10    opaque  10         36        10       2-30    ______________________________________

Consolidation testing establishes that the agglomeration of thenanocrystals is weak enough that agglomerates can be broken down by themechanical energy generated in consolidation. The improvement of thisinvention over other nanocrystal material synthesis inventions can bebest seen by reference to FIG. 9 which shows the pore size distribution,grain size distribution and regularity of pore spacing of titaniumoxide. The data labeled "other" is from titanium oxide generated by theprocess described in U.S. Pat. No. 5,128,081. The unlabeled data is fromtitanium oxide generated by the process in this instant invention. Ascan be seen in FIG. 9A the TEM particle size distribution is muchsmaller and narrower using the process described in this invention. InFIG. 9B is shown that once the nanocrystals are consolidated, the poredistribution of the titanium oxide generated by the apparatus of thisinvention is much smaller than that which is generated by the process inU.S. Pat. No. 5,128,081. In FIG. 9C, the regularity of the pore spacingfurther demonstrates the reliability and reproducibility of the methodof making the nanostructured material. It should also be noted that theproduction rate of the process in this invention is over one hundredtimes greater than the production rate compared to the method set forthin U.S. Pat. No. 5,128,081, making the instant method a commerciallyviable process.

An additional test of the agglomeration is the dispersion of untreatednanocrystal powders which is achieved by applying ultrasonic energy froma sonicating probe (0.2-1 Watts) to a liquid solution (water or ethyleneglycol) that has a 5-50% weight loading of nanocrystals. The ultrasonicenergy forms a colloidal dispersion that remains dispersed and insuspension for a minimum of five months. By treating the solution withadditional liquids, the nanocrystals can remain in suspension for longerperiods of time. This dispersion test determines whether the nanocrystalpowders generated by the process described in this invention are weaklyagglomerated and have high purity and clean particle surfaces.

The following nonlimiting examples set forth exemplary methods ofpreparing nanostructured materials.

EXAMPLES Example 1

A metal rod 1/8"-3" diameter of Ti, Al, Zr, Y, Fe, Cr, V, Cu, Si, Sn, orZn, with a known starting purity (99-99.99% pure) was used as an anodein a transferred arc. The cathode was 2% thoriated-W electrode and wasshielded by 25-100 cfh of a working gas of argon combined with 5-100%nitrogen and/or 5-50% hydrogen. The current of the arc ranges from100-750 amps. The arc creates a plasma tail flame 1-4 inches long andevaporates the anode metal precursor. The 1-200 g/hr of metal vapor isinjected into the plasma tail flame created by the transferred arc. Inthe plasma tail flame, particle nucleation proceeds; and 10-1000 cfhoxygen is injected into the tail flame to form a suboxide species of thestaring metal. The presence of hydrogen from the working gas forms watervapor and produces a fully oxidized material. Further cooling causesmetal-oxide ceramic particles to form due to the presence of oxygen andhigh temperature. Quench gas (1-1000 cfm), in the form of air or theindividual components of air (O₂, N₂, H₂, H₂ O, CO₂), were later addedto further cool the particles and prevent hard agglomeration. Thenanocrystalline powders are collected and typically have primaryaggregate sizes of 1-50 nm and typical agglomerate sizes are 10-100 nm.

Example 2

A metal rod 1/8"-3" diameter of Ti or Al with a known starting puritywas used as an anode in a transferred arc. The cathode was a 2%thoriated-W electrode and was shielded by 25-100 cfh of a working gas ofargon combined with 5-100% nitrogen or 5-50% hydrogen. The current ofthe arc ranges from 100-750 amps. The arc creates a plasma tail flame1-4 inches long and evaporates the anode metal precursor. The 1-200 g/hrof metal vapor was injected into the plasma tail flame created by thetransferred arc. In the plasma tail flame, particle nucleation proceeds;and 10-400 cfh nitrogen was injected into the tail flame to form anitride species of the starting metal. Further cooling causes nitrideceramic particles to form due to the presence of nitrogen and hightemperature. Quench gas (1-1000 cfm), in the form of N₂, Ar or He waslater added to further cool the particles and prevent hardagglomeration. The nanocrystalline powders were collected and typicallyhave primary aggregate sizes of 1-50 nm and typical agglomerate sizeswere 10-100 nm.

Example 3

A metal powder was mixed in a 15-50 wt % loading with metal-oxidepowder. The powders were then compounded into a rod 1/2"-3" diameter bypressing and sintering. The rod was electrically conductive and used asan anode in a transferred arc. The cathode was a 2% thoriated-Welectrode and shielded by 25-100 cfh of a working gas of argon incombined with 5-100% nitrogen or 5-50% hydrogen. The current of the arcranged from 100-750 amps. The anode was evaporated by the arc and 1-200g/hr of the anode vapor was injected into the 1-4 inch long plasma tailflame created by the transferred arc. In the plasma tail flame particlenucleation proceeds, and 10-1000 cfh oxygen was injected into the tailflame to produce cooling and caused formation of metal-oxide ceramicparticles. Quench gas (1-1000 cfm), in the form of air or the individualcomponents of air (O₂, N₂, H₂, H₂ O, CO₂), was later added to furthercool the particles and prevent hard agglomeration. The nanocrystallinepowders were collected and typically have primary aggregate sizes of1-50 nm and typical agglomerate sizes were 10-100 nm.

Example 4

Nanocrystalline powder was made as in Example 1, was uniaxiallyconsolidated in a die and punch arrangement with a pressure of 5-50kpsi. The resulting bulk specimen has a density of 40-50% of its bulktheoretical value. The porosity in the compact has a narrow sizedistribution with pores ranging from 1-50 nm. If the consolidatedspecimen is heated to temperatures near 900° C., the porosity remainsnarrowly distributed and becomes ordered such that pore separationdistance becomes constant throughout the sample. The ordering wasdetectable through the use of small angle neutron scattering (SANS), asshown in FIG. 9D. As shown in FIG. 9C, the ordering results in awell-defined distribution of pore spacings.

While preferred embodiments of the invention have been shown anddescribed, it will be clear to those skilled in the art that variouschanges and modifications can be made without departing from theinvention in its broader aspects as set forth in the claims providedhereinafter.

What is claimed is:
 1. An article of manufacture, comprising:ananocrystalline composite comprising a first nanocrystalline materialcomprising discrete primary particles having a size of about 1-50 nm andan average size less than about 40 nm blended with a secondnanocrystalline material comprising discrete primary particles having asize of about 1-50 nm and an average size less than about 40 nm, each ofsaid primary particles having a substantially spherical shape whereinsaid discrete primary particles are formed within the boundaries of anionized arc extending between a consumable anode and a nonconsumablecathode.
 2. The article of manufacture as defined in claim 1 wherein atleast one of said first nanocrystalline material and said secondnanocrystalline material is selected from the group consisting oftitanium nitride, titanium oxide, yttrium oxide, zirconium oxide,aluminum oxide, iron oxide, silicon oxide, silicon nitride, siliconcarbide, a semiconductor and a metal.
 3. The article of manufacture asdefined in claim 1 wherein said nanocrystalline material comprise fullreacted material having an average size range of about 20-30 nanometers.4. An article of manufacture, comprising:a nanocrystalline materialcomprising discrete primary particles having a size of about 1-50 nm andan average size less than about 40 nm, said primary particles having asubstantially spherical shape, wherein said discrete primary particlesare formed within the boundaries of an ionized arc extending between aconsumable anode and a nonconsumable cathode.
 5. The article ofmanufacture as defined in claim 4 wherein said nanocrystalline materialis fully reacted.
 6. The article of manufacture as defined in claim 4wherein said nanocystalline material further includes agglomerateparticles of size from about 10 nm to 100 nm.